Fire trucks pass the Delta Fire burning in the Shasta-Trinity National Forest, Calif., on Wednesday, Sept. 5, 2018. Parked trucks lined more than two miles of Interstate 5 as both directions remained closed to traffic. (AP Photo/Noah Berger)

REDDING, Calif. — An explosive wildfire that closed down dozens of miles of a major California freeway nearly tripled in size overnight, just weeks after a nearby blaze that left neighborhoods in ruins and killed eight people, officials said Thursday.

The fire that erupted Wednesday afternoon and devoured timber and brush on both sides of Interstate 5 near the Oregon state line had expanded to 23 square miles Thursday (60) square kilometers, prompting mandatory evacuations, the U.S. Forest Service said in a statement. That's up from 8 square miles (21 square kilometers) burning on Wednesday

Authorities did not say in the statement how many people were affected by the evacuation order, but the fire is in a rural area with scattered homes.

The blaze was human-caused, fire officials said, but they didn't indicate whether it was arson or accident.

Truckers abandoned their vehicles Wednesday as flames roared up hillsides. In a video, a passenger in a vehicle screams: "Oh my God, I want to go!" as trees burst into flames and sheets of fire roiled on the side of the roadway.

A firefighter sprays the smoldering remains of a vehicle on Interstate 5 as the Delta Fire burns in the Shasta-Trinity National Forest, Calif., on Wednesday, Sept. 5, 2018. (AP Photo/Noah Berger)

U.S. Forest Service workers helped the driver of one flaming truck to safety and other truckers, firefighters and others aided other drivers, he said.

"There's vehicles scattered all over," Brandon Vaccaro with the California Department of Forestry and Fire Protection told the Redding Record Searchlight. "Whatever occurred here was probably pretty ugly for a while."

About 45 miles (72 kilometers) of the I-5 were closed in both directions, said Chris Losi, a spokesman for the Shasta-Trinity National Forest. The road remained closed through Wednesday night and there was no immediate word on when the lanes would reopen.

The Delta Fire burns in the Shasta-Trinity National Forest, Calif., on Thursday, Sept. 6, 2018. The wildfire closed both directions of Interstate 5. (AP Photo/Noah Berger)

The blaze also delayed Amtrak's Coast Starlight train service between Sacramento and Oregon.

Rural homes and cabins in and around the forest were under evacuation orders, from the community Lakehead north to the Siskiyou County line, Losi said.

"It isn't a lot of people," he said.

The fire was showing "critical" behavior — burning fiercely and moving rapidly — but was still far away from any large towns, he added.

The city of Dunsmuir, with about 1,500 people, was about 15 miles (24 kilometers) from the fire. Residents were issued an evacuation warning, urging them to be prepared to leave if the fire threatened.

A nearby fire in the Redding area burned some 1,100 homes and killed eight people last month. It was only fully contained last week.